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August 09, 2019

Countermeasures for hydrogen gas generation inside the container for high level radioactive waste

Contents

【Current situation】
As for the decommissioning project, waste and fuel debris will be retrieved in the future. Radioactive waste and fuel debris retrieved from the reactor vessel contain water and such water may not be completely removed even with draining or drying.
In that case, the high-energy radiation of the radioactive materials contained in the waste / fuel debris causes radiolysis of water contained in these materials and generates hydrogen gas, which is confirmed from the experience of the accident at the Three Mile Island Nuclear Power Station (TMI-2).
When waste/fuel debris is stored in a storage container for a long time, it is presumed that container will be filled with hydrogen gas. Once the hydrogen gas concentration reaches the lower flammable limit (4%), the soundness of the container may be lost due to hydrogen explosion, or gas discharge due to the increase in the internal pressure may scatter the radioactive materials when opening the container.
Therefore, countermeasures against hydrogen gas generation is required.


【Assumption】
① Releasing hydrogen gas from the container is not acceptable because in doing so, dust-like radioactive material will also be released. A dust capturing function is necessary to be placed in the gas discharge pathway.
② Existing technologies such as catalytic reactions and occluded metals used to suppress the generation of hydrogen gas must satisfy storage management standards (hydrogen concentration less than lower flammable limit (4%) ) ,and also technical proof to ensure the duration of more than 50 years is required.


【Our needs】
In order to solve the above-mentioned problems, We are seeking for technology that has the function of preventing the hydrogen gas concentration from reaching the lower flammable limit without discharging dust from the container

○ Assumed solutions / Technologies (Not limited to the following)
・Filters that permeate only hydrogen gas and reduce radioactive material at negligible amount. (See <Constraints> for details)
・Materials that break down hydrogen gas and maintain hydrogen concentration under the lower flammable limit by enclosing them in a container
・Technological mechanism which suppresses the water radiolysis caused by radioactive materials


【Detailed information】
<Constraints>
○Applicable / Inapplicable proposals
*Applicable proposals
We accept proposals that satisfy all the following requirements.
- The amount of dust released from the stainless steel container must be negligible:
Cs-137, less than 1E-7Bq/cm3
- It is desirable to have the robustness for 50 years or more in indoor static storage conditions.
*Inapplicable proposals
・System which requires off-gas treatment system after extracting generated gas.

○Development Level
The proposal must be at least 5 of the following development levels.
▶︎ 5.commercialized
 4.efficiency verified through feasibility study
 3.feasibility study phase
 2.planning & development phase
 1.idea phase

<References / Documents>
International Research Institute for Nuclear Decommissioning Subsidy Project of Decommissioning and Contaminated Water Management in the FY2015 Supplementary Budgets, Development of Technology for Collection, Transfer and Storage of Fuel Debris, FY2017 Research Report (Only available in Japanese)
http://irid.or.jp/_pdf/20180000_03.pdf
○See below for the retrieval process of radioactive waste and fuel debris from the reactor . (Adopted from page No.126 of the PDF)

Source:Adopted from “Proposal flow for handling fuel canisters”, by IRID, “Subsidy Project of Decommissioning and Contaminated Water Management in the FY2015 Supplementary Budgets, Development of Technology for Collection, Transfer and Storage of Fuel Debris, FY2017 Research Report (Only available in Japanese)”, page No.126 (http://irid.or.jp/_pdf/20180000_03.pdf)

For operation dealing with the target hydrogen gas, please refer to the “Storage area” in the above image.

○Current image of Storage Container size (Adopted from page No.72 of the PDF)
・Vent line (plug) is placed to prevent internal pressure increase.
・The lid structure may change. The shape of Vent line (plug) can be revised but it must not interfere with the hanger.

Source:Adopted from “ Subsidy Project of Decommissioning and Contaminated Water Management in the FY2015 Supplementary Budgets, Development of Technology for Collection, Transfer and Storage of Fuel Debris, FY2017 Research Report (Only available in Japanese) , page No.72 (http://irid.or.jp/_pdf/20180000_03.pdf)


【Submission deadline】
November 30, 2019 (JST)
*Application period and contents are subject to change without notice.
*After suggestion, we may ask you additional questions during the above period.


【Notes】
● Please make sure you read and understand the “Constraints” before your submission. Only proposals that comply with these “Constraints” will be submitted to TEPCO.
● If mandatory questions are not answered or not appropriately answered, the proposal will not be submitted to TEPCO.
● Please move to the submission form from the "Submit" button at the bottom of this page and fill in your proposal.

When you propose your ideas, TEPCO CUUSOO account is needed.
* Please be aware of the submission deadline.

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